Internal combustion engines used in automobiles typically operate on fuel-air mixtures, where a fuel injector supplies fuel and a throttle supplies air. On-board computers, programmed to be responsive to a signal from an accelerator in the automobile, determine the amounts of fuel and air. When a driver wishes to move at a higher speed, he or she depresses the accelerator, signaling the computer to supply more fuel, and more air to the engine. The fuel injectors respond by supplying more fuel and the throttle valve responds by opening wider to admit more air to the cylinders of the engine. When the driver wishes to slow down, the driver lifts his or her foot from the accelerator, signaling the fuel injectors to supply less fuel and the throttle to move to a more closed position.
In most internal combustion vehicle engines, an engine throttle valve is utilized to control the idle speed of the engine. The throttle valve is typically a metal plate that is positioned on a rotatable shaft within the mounting flange or venturi of a carburetor. The metal plate is rotatable to control the amount of air-fuel mixture reaching the cylinders of an internal combustion engine. In many prior art vehicles, the rotational position of the throttle plate may be controlled by a linkage connected to the accelerator pedal of the vehicle. The throttle plate may be positioned in a variety of positions, typically within the range of a wide-open, partially open and closed positions.
In more modern throttles, an electric motor is utilized to turn the throttle plate based on signals from an engine controller, such as an electronic control module (PCM). Various inputs into the PCM, such as the accelerator pedal position and the present position of the throttle, are utilized to calculate the precise amount of adjustment to be made by the motor to the throttle plate to give the engine a desired degree of acceleration. Motorized throttles or so-called “electronic throttles,” often integrate with one or more throttle position sensors (TPS) to monitor the movement of the throttle valve. The sensors relay the varying movement of the throttle valve to the PCM.
When the PCM calls for more air, the shaft rotates in one direction to open the valve. When less air is needed, the shaft rotates in the opposite direction to close the valve. If the motor fails, the air valve or throttle must move to a “default” condition to maintain some level of engine function. A return spring wound onto the shaft during assembly of the throttle typically enables automatic closing of the throttle. When the shaft rotates to admit more air, it winds the spring into a state of torsion, in which the force or bias of the spring opposes the rotation of the shaft in that direction. If the motor fails, the spring biases the shaft in the opposite direction, safely closing the valve.
Due to the dependence on the throttle return spring, should the return spring ever break or become disabled and such failure is not detected, this important default feature would not be available. In order to prevent this condition, a more reliable apparatus for returning the throttle to the default position in cases where the spring is operational or not operational is desired.